June 2018

COVER FEATURE

Neuro-ophthalmology for the anterior segment surgeon
Getting nerve imaging right

by Rich Daly EyeWorld Contributing Writer

Fluorescein angiography characteristics of superficial optic disc drusen (top) and optic disc edema (bottom). Superficial optic disc drusen demonstrated staining, with nodular hyperfluorescence that did not increase in area over time. In contrast, optic disc edema was seen as fluorescein leakage, with increased area of hyperfluorescence over time.

New research shows varying degrees of accuracy among imaging options that aim to identify optic nerve swelling

Even the best imaging technologies can struggle to accurately diagnose some retinal and optic nerve problems.
That was the finding of research published in the journal Ophthalmology that examined the accuracy of imaging reviewed by three masked neuro-ophthalmologists.1
The prospective observational study imaged 19 children diagnosed with papilledema (PE), pseudopapilledema (PPE) owing to suspected buried optic disc drusen (ODD), and PPE owing to superficial ODD. The subjects underwent imaging with B-scan ultrasonography, fundus photography, autofluorescence, fluorescein angiography (FA), optical coherence tomography (OCT) of the retinal nerve fiber layer (RNFL), and volumetric OCT scans through the optic nerve head with standard spectral domain (SD OCT) and enhanced depth imaging (EDI OCT) settings.
Images were read by the masked neuro-ophthalmologists, and the final image interpretation was based on two of three reads. When the image interpretations were compared with clinical diagnosis to calculate accuracy and misinterpretation rates of each imaging modality, fluorescein angiography was found to have the highest accuracy—97%—for classifying an eye as PE or PPE.
The ability of other imaging modalities to accurately distinguish between PE and PPE ranged from 62% with autofluorescence to 74% with ultrasonography.
Accuracy of imaging modalities to identify suspected buried optic disc drusen ranged from 53% for fundus photography to 95% for fluorescein angiography.
The authors found that FA of eyes with PE showed leakage of the optic nerve, while eyes with suspected buried ODD demonstrated no hyperfluorescence, and eyes with superficial ODD showed nodular staining.
They concluded that FA was the best imaging technique for correctly classifying pediatric eyes as PPE or PE. No cases of PE were misinterpreted on FA. Additionally, FA images were interpreted most consistently by the image readers.
Among the other imaging options, fundus photography had the lowest rate—30%—of misinterpretation of PE. The rates of misinterpretation of PE as PPE were much higher for ultrasound, autofluorescence, and all OCT protocols.
All of the imaging modalities except OCT RNFL were better at detecting superficial compared with suspected buried ODD.
Additionally, the study authors warned that the findings indicated that the use of isolated imaging modalities was more likely to lead to misinterpretation of PE as PPE, “which could potentially result in failure to identify a life-threatening disorder causing elevated intracranial pressure and papilledema.”

Why misinterpreted

Stacy Pineles, MD, Jerome and Joan Snyder Chair in Ophthalmology, Stein Eye Institute, UCLA, Los Angeles, and one of the study authors, said the most common reason that optic nerves are misinterpreted as swollen is optic disc drusen. But sometimes congenitally anomalous nerves or optic nerves of very hyperopic children can appear swollen.
When an asymptomatic patient presents and Dr. Pineles is not sure if the optic nerve is swollen, she typically starts with taking a thorough history. She pays special attention to symptoms that might occur if a patient has elevated intracranial pressure, such as headache, nausea or vomiting, diplopia, and pulsatile tinnitus.
“Then I evaluate the optic nerve and look for signs of true optic nerve edema (absent spontaneous venous pulsations, blurring of the vessels as they cross the disc margin, hemorrhage, exudates),” Dr. Pineles said.

Clinical signs

Melinda Chang, MD, assistant professor, neuro-ophthalmology and pediatric ophthalmology, UC Davis Eye Center, Sacramento, California, and a co-author of the study, said among the clinical sign she finds most helpful to confirm accuracy in such cases is the presence of spontaneous venous pulsations.
“Typically, the absence of the blurred vessels at the disc margin is the best sign,” Dr. Chang said.
Among the ancillary testing Dr. Chang recommends are disc photos.
“Disc photos are often useful in small children because you can carefully study every single aspect of the disc, which is hard to do in a moving child,” Dr. Chang said.
She also uses fluorescein angiography whenever possible. Ultrasound is the last resort for her since it’s only positive if the drusen are calcified.
Dr. Chang noted that OCT is helpful in some cases but it also can be misinterpreted.
“The role for OCT is still evolving as technology improves,” Dr. Chang said.